Recently, flat panel displays have been utilized in a variety of commodities and fields. It has, therefore, been demanded to provide a flat panel display with a larger size, higher image quality, and lower power consumption.
Under such a situation in the art, an organic EL (electroluminescence) display device including an organic EL element, which utilizes electroluminescence of an organic material, has received great attention as a flat panel display that is superior in being fully solid-state, drivable at a lower voltage, quick responsive, self-luminescent, etc.
In an active matrix organic EL display device, for example, thin-film organic EL elements are disposed on a substrate on which TFTs (thin-film transistors) are also disposed. In the organic EL element, organic EL layers including a luminescence layer are laminated between a pair of electrodes. The TFT is connected to one of the pair of electrodes. An image is displayed by applying a voltage between the pair of electrodes, thus causing the luminescence layer to emit light.
In the organic EL display device described above, however, the organic EL element may deteriorate due to moisture incoming from the outside. To prevent the deterioration of the organic EL element due to moisture, a related-art organic EL display device proposes a structure in which a moisture low-permeable sealing resin is formed around the organic EL element by the DAM & FILL method, and a desiccant (getter) is filled inside the sealing resin to provide a desiccant layer.
In the related-art organic EL display device described above, however, there is a possibility of impairing pixels or reducing display quality for the reason that, before reaching a full level of moisture absorption ability of the desiccant layer, damage of light emission characteristics caused by moisture may be progressed in pixels in the neighborhood of the desiccant layer, or cracking may occur in the desiccant layer at or near an outer periphery.
More specifically, in the related-art organic EL display device described above, moisture having penetrated through a sealing member (sealing resin) is absorbed by the desiccant layer. However, because the moisture is absorbed into the interior of the desiccant layer without being sufficiently diffused, absorption of the moisture is locally progressed in a region of the desiccant layer at or near the outer periphery more preferentially than in an inner region. Accordingly, the moisture absorption ability of the desiccant layer is saturated in its portion at or near the outer periphery at earlier timing than in the other portion, and intrusion of moisture into the pixels in the neighborhood of the desiccant layer can no longer be suppressed. Hence the light emission characteristics may be damaged. Furthermore, the desiccant layer causes cure shrinkage due to absorption of moisture. However, because the cure shrinkage is locally progressed only at or near the outer periphery, the desiccant layer may be distorted, and the distorted desiccant layer may be cracked eventually. The cracking of the desiccant layer may adversely affect the optical characteristics of the organic EL display device, and further damage the light emission characteristics of the pixels of the organic EL element if a layer including the pixels constituted therein is drawn to displace by the cracking.
To cope with the above problems, Patent Literature (PTL) 1, for example, given below proposes a related-art organic EL display device in which a first resin layer having higher moisture permeability than a second resin layer (sealing member) is disposed between the desiccant layer and the organic EL element. That related-art organic EL display device further proposes arrangements that a first moisture-resistant layer having lower moisture permeability than the first resin layer is disposed between the first resin layer and the organic EL element, and that a second moisture-resistant layer having lower moisture permeability than the first resin layer is disposed between the desiccant layer and the first resin layer. Thus, in the related-art organic EL display device described above, the first moisture-resistant layer is disposed on the organic EL element, and the first resin layer is disposed inside the second moisture-resistant layer. In addition, the second moisture-resistant layer and the desiccant layer are successively laminated inside the first resin layer, and the first resin layer is disposed on the first moisture-resistant layer.
In the related-art organic EL display device described above, because moisture having entered the second resin layer from the outside is not locally present in a peripheral portion of the second resin layer, and is diffused into the entirety of the first resin layer, local moisture absorption by the desiccant layer is suppressed, and the moisture can be uniformly absorbed by the entirety of the desiccant layer. Furthermore, in the related-art organic EL display device described above, the moisture having entered the first resin layer can be more preferentially guided to the side including the desiccant layer than to the side including the organic EL element with the presence of the first moisture-resistant layer, and can be more preferentially absorbed by the desiccant layer. Still further, in the related-art organic EL display device described above, the moisture having entered the first resin layer can be suppressed from being immediately absorbed by the desiccant layer with the presence of the second moisture-resistant layer, and the moisture having entered the first resin layer can be caused to sufficiently diffuse in the first resin layer over its entirety without being localized therein. As a result, moisture can be uniformly absorbed by the entirety of the desiccant layer, and local moisture absorption by the desiccant layer can be avoided.